1. Field of the Invention
The present invention relates to an electrically conducting member for electrophotography, and to a process cartridge and an electrophotographic apparatus which make use of the same.
2. Related Background Art
In recent years, as electrophotographic apparatus are made much more high-speed and long-lifetime, electrically conducting members for electrophotography are sought to have a high durability. Hence, any small changes in physical properties that have not come into question until then cause image difficulties in some cases because of their service over a long period of time. In particular, changes in electrical resistance value have come to be an important factor for the high durability of the electrically conducting members.
Conductive particles such as carbon black and metal oxides which are mixed and dispersed in an elastomer are sometimes used in the electrically conducting members. Such conductive particles are advantageous in that they have so high a conductivity as to cause less environmental variations.
However, such an electrically conducting member with conductive particles dispersed therein makes it difficult in some cases to regulate its electrical resistance value, and comes to be locally non-uniform in electrical resistance value in some cases because of non-uniform dispersion of the conductive particles. Where such an electrically conducting member is used in an electrophotographic apparatus, what is called a pinhole leak occurs in some cases when any excess electric current flows in an electrophotographic photosensitive member (photosensitive member) at its part having a low resistance, to cause faulty images.
To cope with this, as an electrically conducting member having remedied non-uniformity of electrical resistance value, an electrically conducting member is proposed in which an ion conducting agent is added to a polar polymer such as hydrin rubber to regulate the electrical resistance value. However, where the ion conducting agent is used, it has come about that the ion conducting agent ionizes into anions and cations when a direct current is continued to be applied, so that the anions and cations move to come localized, thereby making the electrical resistance value increase gradually.
It has also come about that a low-molecular weight component (e.g., the ion conducting agent) contained in the electrically conducting member may bleed to its surface as a result of coming under an electric field or repeated stress, to cause photosensitive member contamination or the like to make faulty images occur.
As a means for remedying such phenomena, Japanese Patent Application Laid-open No. 2006-189894 discloses that a specific quaternary ammonium salt capable of lowering the electrical resistance value by its addition in a small quantity is used as the ion conducting agent. Japanese Patent Application Laid-open No. 2001-273815 also discloses that a quaternary ammonium salt having an OH group is used in an attempt to keep the ion conducting agent from bleeding.